Hydrocarbon oil containing a mercaptobenzimidazole



Patented June 6, 1 95 I r 2,642,396 I HYDRbCARBON OIL CONTAINING MERGAPTOBENZIMIDAZOLE Thomas C. Roddy, Jr.,Port Arthur,-'lex., assignor to The Texas Compan poration of Delaware y, New York, N. Y, a. cor- No Drawing. Application May 1, 1952, Serial No. 285,551

Claims,

This invention r'elatestd a hydrocarbon or eral oil composition containing a mercaptobenv zimidazole stabilizer which is particularly effective in inhibiting corrosion of metals, such as ferrous metals and copper, in contact with the hydrocarbon oil. "1

This is acontinuation-in-part of my copending application Serial No; 96,139, filed May-28, 19l9,

now abandoned. v

One ofthe principal objects of the'present invention is to provide a superior corrosioninhibitor for hydrocarbon oils including gasoline, kerosine, fuel oil, and lubricating oil.

Other objects and advantages of the invention will be apparent fromf the iollowingdescription and the appendedclaims,

] The problem of internal-corrosion of metal surfaces oi'vessels, pipes, containers, etc, used in the,

storage, transportation, handling and utilization of varioushydrocarbon oils has long been recognized. With the increasing use of pipe lines to transport such finished petroleum products great distances, the problem has been accentuated. Various inhibitors have been proposed for this purpose, and 2 mercaptobenzothiazole has achieved substantial commercial use.

The presentinvention is predicated on the dis covery that the reaction product of ortho-phenylene diamine with carbon disulfide constitutes an unusually 'efiective' corrosion inhibitor for all of the various hydrocarbon oils. In preparing the effective compound, ortho-phenylene diamine mercaptobenzimidazole was then acidified with precipitation of the mercaptobenzimidazole, which latter was separated, washed and dried.

The resulting product is a powdery substance of light t'an to nearly white color, odorless, having abitter taste, with a melting point by the capillary tube method of 297 C. and, after recrystallization from alcohol, of 294 C. The product-is insoluble incold water, Yethylether and dilute hydrochloric acid and shows a positive or slight solubility in hot water, dilute potassium hydroxide-,acetone, methyl alcohol, ethyl alcohol and hydrocarbon oils. 7

In addition tothe:mercaptobenzimidazole set 1 forth above,- the present invention also includes mercapto-a lkylbenzimidazoles of theformula I where R is an alkyl radical containing from 1 to 30 carbon atoms, andm, is a whole number from l to 3 and. represents the number of hydrogens on the benzene nucleus which have been substituted by alkyl radicals. It hasbeen found that such a mercapto-alkylbenzimidazole has the said superior anticorrosive. properties and also has improved solubility in mineral oils over the unsubstituted mercaptobenzimidazole. As examples of these mercapto-alkylbenzirnidazoles, there may be mentioned. the compounds in which in was mixed withcarbon disu-lfide in excess of the fstoichiometric' requirement and the resulting mixture was allowed to stand at room temperature for a period of the order of 24-48 hours with the noticeable liberation; of hydrogen sulfide. The reaction takes place in accordance with the following equations, I q

producing mercap-tobenzimidazole as the active reaction product '(Beilstein, vol; 24,. page 119). The mixture was then agitated with aqueous caustic soda to form the sodium salt of mercaptobenzimidazole, which dissolved in the aqueous layer. The solution was filtered to separate unreacted phenylene diamine, which is not caustic soluble. Ihe resulting aqueous filtrate of sodium C-SH+Ha '45 with carbon disulfide in the manner described the above formula is methyl, ethyl, propyl, butyl, amyl,.hexy1, octy'l, decyl, dodecyl, cetyl, Caz to C30 as obtained from cutsor fractions of propyh ene or butylene polymeryand C20 to C30 as obtained fromparaflin wax; also,the same di-alkyl and; tr'r-alkyl substitutedcompounds, such as v mercapto-diamyl benzimidazole; as-wel'l. as those containing dior tri-substituted dissimilaralkyl groups, such as merca pto methyloctyl, mercaptos butyl dodecyh, and: mercapto-methyl di-t-butylbenzimidazole- In the preparation of these mercapto-alkyl benzimidazoles, the corresponding alkyl substituted o-phenylene diamine is reacted above, since mercaptobenzimidazole has been found' resistant to direct alkylation.

Byway of example, the preparation of a mercapto-mono' t alkyl benzi'midazole, which has been found to be a preferred type of inhibitor, was carried out as follows. In this particular case, the t-alkyl group substituted for a hydrogen atom'on the benzene nucleus of mercaptobenz-im idazole was a t-amyl group. although it is separated from the other isomers obtained in the nitration step. The separated p-tertiary amyl ortho nitro aniline was then reducedby;

hydrogenation in conventional manner to ptertiary amyl ortho phenylene diamine.; The latter was then mixed With'CSZiH EXCESS, of the;

stoichiometric amount, and the mixture allowed to stand at room temperature for 24 hours. The

reaction may be represented a follow i water and soluble in mineral 011s including gasoline and keros'ine, when added in benzene solution, to theextent of at'leastlO pounds per- 1000 barrels of oil. The resulting petroleum solutions were clear and free from cloud.

As an alternate method "of preparation, the mercapto-alkylbenzimidazole may be prepared by alkylating o-phenylene 'diamine with an aliphatic alcohol inthepresence of a suitable Friedel-Crafts catalyst, such as ZnCl'z For example, "o-phenylene' diaminealkylated with lauryl alcohol in thepresence of ZnCl2 gives a mixture of 2-amino-3-lauryl aniline and 2-amino -4-lauryl aniline. The latter compounds, either in admixture or when separated, react with CS2 in the manner set forth above to produce 2-mercapto-4-laurylbenzimidazole and 2- mercapto-5-laurylbenzimidazole. By either alkylating o-phenylen'e diamine under more stringent conditions, or by first alkylating aniline to provide double or triple alkyl substitution on the benzene nucleus with the ortho-position open f by nitration and reduction,'interand followed 7 I be prepared which then react with mediates may CS2 to produce dior tri-alkylated mercaptobenzimidazoles.

- It has been found that mercaptobenzlmidazole or a mercaptoealkylbenzimidazole is more effective as a corrosion inhibitor in various hydrocarbon oils than the best corrosion inhibitors now known and on themarket, of which 2-mercaptobenzothiazole and 2,2'-dibenzothiazol dlsulfide are representative. In addition it has been found that mercaptobenzimidazole is unexpectedly effective as a metal deactivator for the reduction ofthe copper dish gum in cracked gasoline and is comparable to the leading metal deactivators now on the market, of which disalicylidene d1- aminopropane is representative. ,Moreover, the present products are highly effective 'll'l very small amou ts of the order of 0.1 to pounds per thousand barrels of -oil. =While mercaptobenzimidazole has limited solubility in the various ydrocarbon oils, the efiective range is well within the solubility limits thereof. Themercapto-allrylbenzimidazoles are substantially more oilsoluble. The foregoing properties and advantages of the present products areillustrated in the following. tables'which'set forth the results obtained in actual comparative tests of the present :products with the listed compounds in the various hydrocarbon oils enumerated.

f- The fcommercial tests generally employed for determining the corrosion inhibiting effect of the inhibitorin hydrocarbon oils are the copper strip 'corrosion'tests at 122 F. and 212 F. respectively.

In'th'es'e tests,'a sample of the petroleum oil is heated in contact with a copper strip at the stated temperature for a period of three hours. If any discoloration of the copper strip has occurred at the terinination of the test, the same is reported as positive, meaning that the oil is corrosive to copper under the'conditions of the test. The discoloration will varyfrom a light red color for a mildly corrosive stock-to a black color for a more highly corrosive oil; and this discoloration may be' reported on a numerical basis or corrosion index scale varying from 2 for little if any discoloration .to '10 for a black color resulting from a highly corrosive oil." If no appreciable discoloration of the copper strip occurs, the test reported as negative; and the sample is considered non-corrosive to metals-under-the conditions of the test. It has been found that certain oils which are noncorrosive to copper in the test at 122 F; may result in-objectionable corrosion when transported through pipe lines over long periodsof time, or when used in certain metallic equipment where long service life is essential. For this reason, the more rigorous copper strip corrosion test at 212 F. is also employed as a measure of the effectiveness of the inhibitor in oils to provide the ,re quired protection for such long service life. t Inthe following Table I, a Stoddard solvent (kerosine) having typical tests of 18.5 APIgraw ity,- F. flash point, and 328-380 F. distillation range was admixed with free sulfur in the proportion of 0.35Ygramto 56 liters of the kerosine. Samples. of this corrosive stock were then subjected to comparative copper strip corrosion tests at 122. F. and 212 F. with various inhibitors. All tests on the inhibited samples containing from 1 .to 20 pounds of inhibitor per thousand barrels of lrerosine were negative in the copper strip corrosion test at 122 F, However, the following results, showing difierences in the effectiveness of till; inhibitors, were obtained in said test at 2 .F.:

' TABLEI Stoddard solvent+0.35 g. free sulfur per 56 liters Dosage, C Corro- Ol'l'OSlOR- Inhibitor per Cu strip M at 212 F barrels Scale 0 Positive... 6% 1 ..--do. 5 5 ..--.do.-.- 5 10 do... 5 20 .....do.... 5 1 .....do 5 5 do-.-- 5 10 .....do.... 5 20 ...-.do 5 1 Negative.. 2 6 ...do 2 10 Positive... 2 20 .do-.-- 2% per thousand barrels is capable of giving a negathis result in therigorous test at 212 F., whereas the other listed inhibitors, which have heretofore been considered to be the best for this purpose,

are incapable of preventing copper striprcorro-e sion, even when employed in considerably larger proportions .Inthi's and; the following tables:

dealing with gasolines andv kerosines, it should-be explained that, while the tables. show the mercaptobenzimidazole addedin proportions of to. pounds per thousand barrels, not all ofthel added inhibitor went into solution in thelight oil in these cases; In fact, a proportion as small as" 5 .pounds per thousand barrels gave an appreciablesediment of undissolved inhibitor in some cases thus showing that the inhibitor is highly effective in very minute concentrations I In the following Table II, a water white kerosine with typical tests of 42.9" API gravity, 136 F. flash point, and 332-512 F. distillation range was employed as the base stock. To this base stock was added sufficient free sulfur to render the kerosine highly corrosive to the copper strip corrosion test at 212 F. Samples of thishighly test The latter is ordinarily conduotedin conjunction with the copper dish gum. test, which. is

a measure of'the gum stability of the. gasoline v in. Sto age and of the tendency of the gasoline to deposit gum in fuel systems. containing ;cop:- per. In the copper dish gum test, ml. of, the gasoline sample are placed in a highly-polished weighed copper dish and the latter is mounted on a steam bath at 99.5-l00 C. under a hood with air circulation o-verthe top of the sampleuntil it has evaporatedto dryness. Then the dish is,

Placed in an oven and heated at IOU-C. for

about /2-1 hours until no appreciable further loss-in weight; occurs. The-dish is then cooled in.:a-'desiccatorand weighed. The increase in Weight is reported asmilligrams of gum per;;100

ml.-,o-f sample, It will be noted thatthis is-a catalyzed, test and, in conjunction with other tests asv discussed hereinbelow, serves to distinguish. Inetalideactivators from antioxidants,

.The copper dish corrosion test is run in the same manner exceptthat the appearance of the dish or cupused for the test is observed to indisulfur-or corrosive sulfur compounds. A grey to corrosive kerosine were then inhibited with the indicated amounts of the various inhibitors and subjected to comparative copper strip corrosion tests at 212 F. with the following results:

TABLE II Water white Icerosinle+free sulfur cate the presence in the gasoline of elemental black discoloration of the inside of the dish is reported as positive. Lack of; corrosive discolor ation is reported as negative. The extent of corrosion may be reported on a numerical scale.

termed the estimated corrosion index in a manner similar to the copper strip corrosion indexscale discussed above.

The following results were obtained in comparative tests on a gasoline, which also show the superiority of mercaptobenzimidazole as a corrosion inhibitor. A heavy straight run gasoline having a boiling range of -410" F., obtained Dosage, Corrosion- Inhibitor lbs. per 011 strip 5%; of

' M bbls. at 212 F. P

None 0 Positive Black, Z-mercapto benzothiazole 5 do Black and Brown. Do l0 .do l Do.- 2,2dibenzothiazol disulfide. 5 .do. Do. i

Do 10 .doi Red and Brown. Mercaptobenzimidazole 5 do. Golden Do l0 do. Do.,

1 Strips were borderline with respect to passing this test.

Here again, the mercaptobenzimidazole was ployed. for gasolines is the copper'dish corrosion Another corrosion test which is frequently emfrom a high sulfur crude, was acid treated with 12 pounds per barrel of used alkylation acid (about 88% of H 804) and then doctor sweetened. The resultant gasoline after treatment containedpolysulfides and motor fuel blends con-f taining only a smallproportion ofthis hibited straight run stock were highly corrosive,

producing a very black copper cup when the above described copperdish gum test was made. Tests made on this treated corrosive stock by the above described copper dish corrosion te'st, with and without the addition of the specified inhibitors in the indicated amounts, gave the following results:

. TABLE III Heavy straight run gasoline from V I is high sulfur crude i Est.

Dos Inhibitor lbs. per gg ggg Apearance of Cup M bbls. Index 'None, 0 Positive" Black. Z-mercapto benzothiazole 5 d Peacock to black.

Do 10 Do. Do 20 Do.

2,2 dibenz'o iazol disulflde 5 Brown with much precipitate. Do 10 Brown with some precipitate. Do 20 Brown-much improved. V

Mercaptobenzimidazole 5 Golden with white precipitate. 130.. 10 Do. Do.. 20 Do.

i are assigned, this means the dish was unevenly discolored.

7i. In further explanation of the foregoing table. the copper cups from the samples inhibited with 2-'-mercaptobenzothiazole were peacock-colored around the upper rim which was only momentarily in contact with'the corrosive sample, While by far th'elargerpart of each cup was black. On the other hand-the copper cups from the samples inhibited with 'mercaptobenzimidazole had no discoloration around theupper rim. while the balance of-each cup had only a faint golden discoloration, indicating only slight corrosiveness of the copper by this inhibited gasoline which was initially highly corrosive. v

In addition to the lighter distillates', the inhibitors of the present invention are also outstandingly superior as corrosion inhibitors in intermediate and heavy oils, including gas oils, fuel oils and lubricating oils. In the following Table IV, a sweetened diesel fuel, having typicaltests of 38.1 -API gravity and 410-618 F. 1 distillation range, was selected as'th'e base stock for comparative tests. The uninhibited samples of this diesel fuel were highly corrosive in the copper strip corrosion tests at both 122 F. and 212 F. All of the inhibited samples were negative in the copper strip corrosion test at 122 F. However, the'following results were obtained on the inhibited samples in the copper strip corrosion test at TABLE IV V Sweetened diesel fuel oil and gear oils. Thus, a commercial cutting oil was selected, having the followingcomposition':

I Q 1 Percent by" weight Paraffin base lubricating 011 s. U. s. vis. at

- 100. F. of 95+105 20.0

Paraiiin base lubricating oil S. U. S. vis. at

Sulfurized and chlorinated diisobutylene with: i-

or content of 19-22% and 01 S content of 22-25% 1.5 Lecithin 0.1

z mercaptobenzothiazole 7 0.1

Each of the two viscosity grades of lubricating oil in the above productwas produced by distilla-- tion, lig'htto moderate'acid treatingheutraliz In place of the tively.v However, the higher proportion did not completely dissolve, and the excess or suspended portion of the inhibitor was filteredout so that Appearance 7 of Strip Black. Reddish Brown.

Do. Golden Red. E Slight Golden.

very slight transparent discoloration.

' The inhibitor of the present inventionis also effective in lubricating oils and compounded lii bricating oils, where the specifications require non-corrosiveness in the copperstrip corrosion tests. This applies, for example, to cutting oils, premium and heavy duty motor and dieseloils,

1 After closer examination, the strips were judged satisfactory and passabledue to in" the following- Table V these samples are reported as containing 0.01+% of the inhibitor. Comparative copper strip corrosion tests at 122 F. and 212 F. on these blended cutting oil samples gave the following results:

TABLE V Combined sulfur and chlorine containing cutting oil I J v Congsion-Ou C r P t Q r I I Y s Inhibitor gfta 1 Color 2-mercaptobenzothiazole 0. 1 N 2 Bright.

0.1 P05... 8 Dark Brown. 0.01 Neg... 2 Bright. 0.01 Pos 3 Slight tarnish. 001+ Neg 2 Bright. 1 0. 01+ Pos.-. 3 Slight tarnish.

l Limltof solubility somewhere between 0.01 and 0.05%.

weight is roughly equivalent to about 30 pounds 5 per thousand barrels; and in products containsulting sweetened gasoline blend were then inhibitedwith a conventional gum inhibitor (antioxidant) and certain f the samples were also provided with a corrosion inhibitor and subjected to ASTMinduction'period and copper dish corros ion tests as shown in the following table:

TABLE VII Blend of heavy S. R. and cracked gasolines Gumvhihibitor Corrosion Inhibitor ASTM. lii ductilon gu Dish Dosage Dosage er o 011051011 Type #/M bblv Type #/M bbl. 7

No.1 30 o 395 positivea I v black. D0 40 0 490 Do. "Do.'- -50 0 565 Do U Do. 30 2-mercapto benzothiazole. 395' Do D v 30 i -d0 360 Do.

mercaptobenzimidazole 5 v 420 negativegolden. Do. 7, 30 do i. 10 420 Do.

'4 J Composition of gum inhibitor No. 1:

" 1*o;ni-i-1n-, 03 "42 wBy weight, percent C4He NH* NH 4H o 6 st ventlniv ing a lubricating oil base, the inhibitor is generally employed within a'range of about 560 pounds pervthousand barrels, with about 15-30 pounds per thousand barrels being preferred.

As a further illustration of the effectiveness of the present product as a corrosion inhibitor in a heavier lubricating oil, the following table sets forth the results obtained on a premiumtype motor oil stock of S. A. E. 20 grade to which was added a small amount of sulfurto render theoil highly corrosive in the copper stripcorrosion test at 212 F. The said motor oil stock was prepared from a paraihn base wax distillate by furfural refining, light acid treating, clay contacting and solvent dewaxing.

TABLE VI' iParajfin base motor oil .stoclc bbls. blended at room temp. ior 30 min.

, As shown birthe foregoing table, improved r.e-;

sults were obtained by blending the mercapto-= 5g benzimida zble in the lubricating oil without heating. g 4

A heavy straightrun gasoline fromhigh sulfur.

crude of the character set forth abovein Table III was mixed with a blend of thermally cracked 3 gasolines in the proportion of about 1 1.7% by volume of the heavy straight run to 85.3% of thethermally cracked gasoline blend. The thermally cracked gasoline blend had typical tests of 90-382", F. distillation range, with a point 7 of 247 F., API gravity of 59.2, bromine number of 52 and acid heat of 98 F. The resultingblend was-sweetened, thereby utilizing the free sulfur in the heavy straight run as a portion of the sulfur the sweetening step. Samples of the re- The ASTM induction period. test (AST Method D525-46) isa determination of the stability of gasoline under accelerated oxidation age. In this test a 50 ml; sample is "placed in a bomb which isvfilled with oxygen at pounds per square-inch at 15-25 C. The bomb is then placed in a boiling water bath and maintained at 98-102 C. The pressure isread at stated intervals and recorded continuously until the socalled break point'is reached. The latter'isflthe point in the pressure-time curve that is preceded by aIpressui-e drop of 2 lbs. per square inch 'with'-' in'1'5 minutes and succeeded by a drop of not less than'2'pounds per square "inch in the following 15minute's. The'induction period'is reported as thetime in minutes elapsed between the placing of the bomb the bath and the break'poin't. It will be noted that this is an uncatalyzed'test and whenconducted on a gasoline sample which is free from dissolved copper or other catalytic metal or metal compound, is ameasure of the eifect'ivenessof the ee-called gum inhibitors as antioxidants, as opposed to metal deactivators. A substantial increase in thelength of the induction period is indicative of agood antioxidant h'ithis'test.-"

From the foregoing Table-VIL -it will'be notedthat theblend of heavy straight run and cracked gascline was' highly corrosive in "the copper dish corrosion test and that this corrosion could not be controlled by the use of the'well known corrosion inhibitor; 2-mercaptobenzothiazole; On the other hand m'ercaptobenzimid-azole was efiective in giving a negative result in this corrosion test without interfering with-orreducing'the eife'c 'tiveness'o'f the conventional guminhibitor. -In

1,2-diaminopropane, gave ASTM induction .pe-

l l riods oi405 minutes and 415 minutes. respectively, thereby indicating the mercaptobenzimidazole to be at least comparable to this known outstanding metal deactivator in this test.

Further tests on blends of sweetened thermally cracked gasolines having the characteristics of those set forth above gave the following results:

TABLE VIII 1ST BLEND OF THERMALLY CRACKED GASOLINES 2ND BLEND OF THERMALLY CRACKED GASOLINES None l25 25 Gum Inhibitor No l 10 210 8 30 340 6 Gum Inhibitor No 10 300 7 Do 30 340 12 Metal Deactivator No. 1- 135 10 10 0 10 120 12 16 Mercaptobenzimidazole 10 120 6 14 Do 30 120 7 17 1 Para di-butylphenylenediamine, CaHq-HN Nil-0 H I 80% disalicylidene 1,2-diaminopropane+20% xylene.

Inthe foregoing table, the initial copper dish gum test was made on the blends as freshly prepared, and the one month tests were made on the blends after conventional storage for that length of time. The foregoing Table VIII shows that mercaptobenzimidazole is highly efiective in reducing the initial copper dish gum and improving the stability of the gasoline on storage. This is quite evident from the tests on the first blend of the table, since that inhibited blend was highly unstable in the presence of metal catalysts as shown by the substantial increase in the one-month copper dish gum over the initial. From these results it appears that mercaptobenzimidazole shows an apparent initial efiec tiveness as a metal deactivator in addition to functioning as a superior corrosion inhibitor; but on storage for periods of severalmonths or more involving an unsaturated gasoline, this apparent metal deactivating effect is lost and the compound may even function as a gum accelerator.

The following tests show the effectiveness as a corrosion inhibitor for mineral oils of a typical mercaptoalkylbenzimidazole in comparison with conventional inhibitors and also with the unsubstituted mercaptobenzimidazole. V

In the following Table IX, a water white kerosine with typical tests of 43.0 API gravity, 125 F. flash point and 335-515 F. distillation range was employed as the base stock. Samples of this particular corrosive kerosine were then inhibited with the indicated amounts of the listed inhibitors and subjected to comparative copper strip corrosion tests at 122 F. and at 212 F. with the following results:

HHRO cow-c TABLE IX Water white kerosine Cu Stn'p Corrosion Dosage, Index at Inhibitor lbsJM None 6 7 Z-mercapto benzotln'azole 5 l 5 0 10 1 6 2, 2-dibenzothiazol disulfide 5 l 5 Do 10 1 5 Alkyl MBI 1 5 1 1 Do 10 l l l 2-mercapto5t-amylbenzirnidazole.

This shows the mercapto-alkyl benzimidazole to be unusually efiective in comparison to the conventional inhibitors, since the former completely inhibited corrosion in the test at 212 F., giving a corrosion index rating of 1.

An additional batch of water white kerosine with typical tests of 43.6" API gravity, 129 F. flash point, and 336-516 F. distillation range was made highly corrosive by the addition of free sulfur. Samples of this highly corrosive kerosine were then inhibited with the indicated amounts of the listed inhibitors and subjected 1 2-mercapto-Bt-amylbenzimidazole.

In order to test the storage stability of the mercapto-alkylbenzimidazole, samples of a similar water white kerosine containing added free sulfur, together with the indicated amounts of inhibitor, were stored in 5 gallon metal drums for periods of 3, 6 and 12 months. The samples were tested for copper strip corrosion at 212 F. at the end of those periods with the following results:

TABLE XI Water white kerosine free sulfur Inhibitor None .Alkyl M1311 Dosage, lbs/M bbl 0 1 2 5 10 Cu Strip Corrosion Index at In a1 7 7 6 4 2 1 7 6 6 Neg. Neg 7 6 6 6 3 1 2-rnercapto-5t-amylhenzimidazole.

These results show that the inhibitor is slowly depleted in the presence of free sulfur. A dosage of 5 pounds per thousand barrels was Sllf". ficient to maintain the base stock satisfactorily,

portationu ti'o'nal: inhibitors are ineffective :initially;.in this test at 212 F. The results show thatsba'se stocks,

which-,arehighly corrosive due tothe presence' of ireesulfur, can be satisfactorily inhibited'against corrosion .by' the mercapto-alky1benzimidazole for normal periods of storage and pipe line trans- 'Similar corrosion and storage tests were made on "an essentiallysaturated aviation gasoline containing a mixture of straight run-gasoline and alkylate and having aidistillation range of 110-- 320 F.. Samples. of the gasoline containing the indioatedi'amounts of the'listed inhibitorswere stored: in brown glass .bottles oven-Water and iron..:lCopper. trip corrosion tests at 212 F. were 9 Aviation gasoline Q 5 5' 'GuStrip Oorrosion Iudex p r Dosage. I at 212,E, lnhibitor Nibgil Int; .12 c.. H n l, 3mo. 6111c.

None 5 6 7 8 2-mercapto benzothiazoleun 1 6 6 6 7 Do 5 5. 5 5 6 Do 10 4 6 5 4 2,2 dibenzothiazol disulfide 1 5 5 6 10 4 5 6 5 l l 6 '6 7 2 1 '6 5 4 5 1 2 1 4 10 1 2 '1 4 O 6 6 7 Y 6 0.25 2 6 7 6 l 1 Neg. 7 6

1 2-mercapto-5t-amylbenzimidazole.

Here again the conventional inhibitors were ineiiective initially. On the other hand, both the mereaptobenzimidazole and the mercapto-alkylbenzimidazole were completely efiective initially on this corrosive aviation gasoline which had Due to the relativeinsolubility of gone off test. the mercaptobenzimidazole in this particular gasoline, a maximum dosage of around 1 lb. per thousand barrels could be added in order to maintain a clear solution. This proved suiiicient to satisfactorily inhibit the stock for aperiod of at least three months, although inhibitor depletion had occurred by the end of six months. The mercapto-alkylbenzimidazole on the other hand maintained a clear solution in the aviation gasoline with a dosage up to 10 lbs. per thousand barrels; and dosages of 5 and 10 lbs. per thousand barrels were completely effective over a period of six months.

The foregoing results on inhibitor depletion on storage represent rather severecases. It has been i a 7 for the usual periods of storage and transportaportation involved. :In the-heavier hydrocarbon oils, the inhibitor of thepresent invention may be used within the'range' from about 0.1 to pounds per thousand'barrels, and generally about 10-30 pounds per thousand barrels. As noted above, mercaptobenzimidazole is more soluble in the heavier hydrocarbon oils; while solubility is not a problem with the mercapto-alkylbenzimidazole within the proportion ranges generally employed. The inhibitors of the present invention are universally effective as corrosion inhibitors torthe various types of finished hydro carbon oils which aretransported through the prqdfidt pipe lines.

Obviouslyj many"modifications and variations of theinvention, as hereinbefore set forth, may bemade without departing from the spirit and scopethereof and, therefore, only such limita tions'should be-imposed as are indicated in the ppended claims.

"'Iclaimi' l. A mineral hydrocarbon oil normallyfcorro sive to metal in the presence of sulfurcontaining a corrosion inhibiting amount within the of 0.1 to 60 pounds per thousand barrels of oilof a corrosion inhibitor selected from the group consisting ofmercaptobenzimidazole and alkyl substituted derivatives thereof having the formula o-sn where R. represents any alkyl radical containing from 1 to 30 carbon atoms, and n is a whole number'from' 1 to 3 and represents the numberof hydrogen atoms on the benzene nucleus which have been substituted by any alkyl radical or radicals represented by R.

2. A mineral hydrocarbon oil according to claim 1, wherein the corrosion inhibitor is mer- 5. A light petroleum oil normally corrosive to.

copper containing 0.1 to 30 pounds per thousand barrels of the light oil of a corrosion'inhibitor effective to inhibit said corrosionselected from tion. However, in the case of unsaturated stocksf.

such as cracked gasoline, inhibitor depletion occurs more rapidly; and, for this reason, the

mercapto-a1kylbenzimidazoles are preferred due to their increased solubility, with resultant inthe group consisting of mercaptobenzimidazole and alkyl substituted derivatives thereof having the formula where R represents any alkyl radical" containing from 1 to 30 carbon atoms, and n is a whole have been substituted by any alkyl radical or radicals represented by R.

6. A light petroleum oil'according to claim 5, wherein the corrosion inhibitor is mercaptobenzimidazole."

"74A light petroleum..oi1 according to'claimb, wherein the corrosion inhibitor is a mercapt alkylbenzimidazole.

-8. A light petroleum oil according to claim '7, wherein the corrosion inhibitor'is 2-.mercap-tofite-amylbenzimida'zole. I I- 93A gasoline containing 0.1 to 30 pounds-per thousand rbarrels'of a corrosion inhibitorsselected from the group consisting of me'rcaptobenzimidazole and alkyl. substituted derivatives thereof having the formula 16 '13. A diesel fuel comprising a mineral oil distill-ate within the gas oil range containing mercaptobenzimidazole in an amount within the range of 0.5 pound per. thousand barrels up to the limit of solubility of the mercaptobenzimidaz'ole in the oil. 7 14. A mineral lubricating oil normally cor,- rosive to copper in the copper corrosion test at 122 F. containing a corrosion inhibiting amount of mercaptobenzimidazole within the range of 5-60 pounds per thousand barrels of the oil. 15. A cutting oil comprising as the essential ingredients a mineral lubricating oil in major amount, a sulfur and chlorine containing additive in minor amount efi'ective to improve the cutting properties of said oil, and a small proportion of mercaptobenzimidazole within the range of 5-60 pounds per thousand barrelswof oil effective to substantially inhibit said cutting oil against metal corrosion. Y THOMAS C. RODDY, JR.

References Cited in the file of this atent UNITED STATES PATENTS 2,382,906 Pedersen Aug. 14, 1945 

1. A MINERAL HYDROCARBON OIL NORMALLY CORROSIVE TO METAL IN THE PRESENCE OF SULPHUR CONTAINING A CORROSION INHIBITING AMOUNT WITHIN THE RANGE OF 0.1 TO 60 POUNDS PER THOUSAND BARRELS OF OIL OF A CORROSION INHIBITOR SELECTED FROM THE GROUP CONSISTING OF MERCAPTOBENZIMIDAZOLE AND ALKYL SUBSTITUTED DERIVATIVES THEREOF HAVING THE FORMULA 